This invention relates to a non-aqueous electrolyte cell and, more particularly, to an improvement in an anode thereof.
A demand is raised for a cell of a higher energy density of keeping with miniaturization of electronic equipment. For meeting this demand, a variety of non-aqueous electrolyte cell, such as so-called lithium cell, have been proposed.
However, the cell making use of lithium metal in the anode, especially when used as a secondary battery, has the disadvantages that
(i) 5 to 10 hours are usually required for charging, and the quick charging of the cell is rather difficult and
(ii) cyclic service life is short.
These are caused by the lithium metal itself and the main causes are said to be the changes in the lithium form, formation of dendritic lithium and irreversible changes of lithium, brought about by repeated charging and discharging.
As one of the means for overcoming these deficiencies, it has been proposed to use the carbonaceous material in the anode. This takes advantage of the fact that the compound of the intercarbon layer of lithium may be formed easily electro-chemically. For example, when charging is performed in the non-aqueous electrolyte solution, with the carbon as the anode, lithium in the cathode is electro-chemically doped between the carbon layers of the anode. Lithium-doped carbon acts as the lithium electrode and lithium is undoped from between the carbon layers with progress of discharging to return to the cathodes.
Meanwhile, since the current capacity (mAH/g) per unit weight of carbon is determined by the amount of doped lithium at this time, it is desirable that the doped amount of lithium be as large as possible at the anode (theoretically, the upper limit is one Li atom per six carbon atoms).
Heretofore, the carbonaceous material of the anode having the interplanar distance of the (002) plane of the order of 3.40 to 3.60 A and the density of the order of 1.70 to 2.20 g/cm.sup.3 is used, as disclosed for example in U.S. Pat. Nos. 4,702,977 and 4,668,595.
However, with such carbonaceous material, the amount of doped lithium is insufficient and of the order of only about half the theoretical amount.